Adjustable-pitch axial fan

ABSTRACT

An arrangement for adjusting fan blades 2 exchangeable in operation. The adjusting means comprises a compressed air box 5a, 5b for actuating each fan blade by means of a dog member 5, said box 5a, 5b and said member 5 being nonrotatable on the fan wheel axle 3. The fan is easy to adapt to different demands for capacity due to the fact that fan blade shaft 2a is made of a number of exchangeable preselected standardized sizes 18, 19, 20 and always has the same above mentioned arrangements for the rest of the fan.

United States Patent 1 Siiterdal Oct. 29, 1974 1 ADJUSTABLE-PITCH AXIAL FAN [75] Inventor: Edgar Siiterdal, Rottne, Sweden [73] Assignee: Aktiebolaget Svenska Flaktfabriken,

Nacka, Sweden [22] Filed: Mar. 27, 1972 [21] Appl. No.: 238,559

[30] Foreign Application Priority Data 3,543,368 12/1970 Marlow 4l5/D1G. 3 3,603,698 9/1971 Jensen 416/157 FOREIGN PATENTS OR APPLICATIONS 155,043 11/1938 Austria 416/205 467,096 1914 France 416/168 1,095,454 12/1960 Germany 416/157 674,657 6/1952 Great Britain 416/157 916,310 l/1963 Great Britain 416/157 1,011,419 12/1965 Great Britain 416/157 Primary Examiner-Everette A. Powell, Jr. Attorney, Agent, or FirmDorfman, I-Ierrell and Skillman 5 7] ABSTRACT An arrangement for adjusting fan blades 2 exchangeable in operation The adjusting means comprises a compressed air box 5a, 5b for actuating each fan blade by means of a dog member 5, said box 5a, 5b and said member 5 being nonrotatable on the fan wheel axle 3. The fan is easy to adapt to different demands for capacity due to the fact that fan blade shaft 2a is made of a number of exchangeable preselected standardized sizes l8, 19, 20 and always has the same above mentioned arrangements for the rest of the fan.

1 Claim, 4 Drawing Figures T29l974 3,844,680 PATENTEU SHEET 2 or 2 This invention relates to an arrangement adapted at an axial fan equipped with a plurality of blades adjustable in operation to act upon the adjusting by means of a dog member rotating with the axial fan impeller and simultaneously axially displaceable in relation to said impeller, which dog member is supported on a bearing means separated from the drive shaft of the axial fan impeller, and comprising means for causing each of the fan blades to assume a corresponding setting position responsive to the axial displacement of the dog member, and provided with a preferably semi-spherical impeller casing covering the hub of the axial fan and said dog member and the bearing thereof. The invention further relates to a novel method of manufacturing such an axial fan.

Arrangements for adjusting the fan blades of axial fan impellers in operation are known previously. Their adjusting means usually were designed as a disk inserting into the hub of the fan impeller and having a thickness sufficient to receive in a groove a ball-shaped pin mounted on a radially projecting arm of each fan blade. A combination of worm gears and racks has been utilized for actuating the adjusting means. Adjusting means of the aforesaid kind, however, are heavy, relatively expensive and require much space. Their construction further involves a large gyrating mass, so that for each definite size of rotation of the fan blades large motions of the adjusting means are required and the rotary parts have to meet high requirements with respect to balancing. A further disadvantage of said conventional construction of the adjusting means are the high strains on the bearing means. The present invention has as its object to eliminate the shortcomings of the conventional adjusting means. The novel construction has the advantage of having a light weight, small structural dimensions in the axial direction and a low moment of gyration. The axial fan impeller according to the invention, therefore, can be mounted directly on the axle journal of the drive motor even at small effects.

The arrangement according to the invention is characterized in that each fan blade at its end facing the hub portion and said impeller casing is formed to a bearing housing and provided with a blade cover mounted rotatably by said axial bearings on a blade axle secured in the hub of the axial fan impeller, and that each blade cover by means of an arm provided in a point of the circumference of the blade cover and in a point on the outer circumference of the dog member is connected with the dog member for turning the blade cover and thereby the blade through an angle determined by the axial displacement of the dog member, and that the dog member comprises a compressed air box connected to a compressed air line for the supply of compressed air to the interior of said compressed air box for axial displacement of the dog member, preferably against the action ofa spring returning the dog member at reduced air pressure.

An expedient embodiment of the arrangement is characterized in that one wall of the compressed air box is a diaphragm of a flexible tight material.

A particularly advantageous embodiment of the arrangement is characterized in that each blade is mounted in a single axial ball bearing disposed in the outer end of the blade axle fixed in the hub of the axial fan impeller, and that the axial pressure required for positioning the fan blade at the standstill of the axial fan impeller, which pressure in operation is produced by the centrifugal force acting on the blade, is produced by a spring, in the form of a spring washer. This embodiment renders possible a compact and particularly space saving construction with very moderate strains on bearing means and balancing arrangements.

The invention includes also a novel and improved method for manufacturing axial fan impellers of different sizes of the aforesaid kind. The method is characterized in that the fan blades are of one and the same size while the blade axles and impeller casings are selected from series of a limited number of standard sizes. This method is highly adapted to render the manufacture of the fan details cheaper and their storage simpler.

The invention is described in greater detail in the following, with reference to the accompanying drawings illustrating an embodiment of the arrangement according to the invention and showing a schematic example of the application of the method for manufacturing axial fan impellers of different sizes of the kind here referred to.

FIG. 1 shows in its upper parta section through the arrangement,

FIG. la shows on an enlarged scale the special mounting of the fan blade,

FIG. 2 shows the fan blade in a setting turned through FIG. 3 illustrates a method according to the invention for the manufacture of axial fans of standard elements.

position In the Figures, 1 designates collectively an axial fan intended, for example, to transport fumes from an industrial plant. 2, 2' designate a fan blade in two different positions with an angular difference of 90 after having been turned about a blade axle 2a. 2b designates a holding means for each fan blade, the axle of which in the embodiment here referred to is presupposed to be secured on the hub 3a and be movable about the outer end of said blade axle 2a. The fan blade, therefore, is formed to a bearing housing 13 closed by a blade cover 13a, whichis provided with a hole for said blade axle 2a.

In said bearing housing 13 is provided an axial bearing 15 with a chamfered limiting surface, which bearing according to the invention is associated with a support ring 15a, which also is provided with a chamfered limiting surface. By the novel and improved arrangement according to the invention, owing to its light-weight construction, small structural dimensionsin axial direction and low GD -value, it has proved possible to solve said control and bearing problem by a single axial hearing of the above design. The axial pressure required for positioning the fan blade 2 at the standstill of the axial fan impeller l, which pressure in operation of the axial fan is produced by the centrifugal force acting onfthe fan blade, here is produced by a spring washer lo, the appearance and position of which mostclearly is shown in FIG. 1a.

4 designates a bearingmeans for the dog member 5 according to the invention, said member. being a compressed air box with walls 54, 5b and with a mounting shown at 5c. One wall 512 of the compressed air boxfis a diaphragm 5b of a flexible tight material, for example plastic or leather. The dog member 5, i.e. the cornpressed air box, is connected to a compressed air line 6, and 7 designates a connecting fitting for said line. The axial displacement. in the direction of the double arrow 10, is effected against the action of a spring 8, and the motion during the displacement is controlled by a pin 9. Said spring 8 is located between the outer wall 50 of the dog member and a housing 11 for the axial fan impeller. 17 designates a conventional cylindric casing around the fan impeller. The arrangement according to the invention for adjusting the fan blades 2 is illustrated in two different setting positions in FIG. 1 and, respectively, FIG. 2. In the first position shown the fan blade is designated by 2, and in the latter position turned through 90 the corresponding fan blade is designated by 2. FIG. la shows on an enlarged scale the relative arrangement of the root of the fan blade 2, part of the blade axle 2a, the balancing element 14 and the axial bearing 15 with associated supporting ring.

Designations of details shown in the Figures 1 axial fan 2, 2' fan blade in different setting positions 20 blade axle,

2b holding means for 2a 3 drive shaft for axial fan 30 hub for axial fan 4 bearing means for dog member 5 dog member 5a,5b walls of 5,

5c mounting for 5 6 compressed air line connecting fitting for 6 8 spring means 9 control pin for dog member 10 axial motion direction for dog member 11 casing for axial fan impeller 12 adjusting arm 12a,l2b holding bolts for 12 13 bearing housing with blade cover 13a blade cover 14 balancing element 15 axial bearing (with chamfered limiting surface) 15a support ring for 15 (with chamfered limiting surface) 16 spring washer 17 cylindric casing for fan 18 blade axle for axial fan, type l 19 blade axle for axial fan, type II 20 blade axle for axial fan, type III I claim:

1. An apparatus for effecting axial flow comprising a generally cylindrical casing, said casing being selected with a diameter corresponding to the desired size of fan, a rotary fan mounted coaxially in said casing having a rotary hub adapted to be mounted on the end of a drive shaft and a plurality of radial fan blades, means to change the pitch of said blades during operation including a dog member mounted outboard of said shaft end rotatable with said hub and displaceable axially relative thereto, and means connecting each of said fan blades to said dog member to determine a pitch position responsive to axial displacement of said dog member, each of said radial fan blades having at its inner end a housing cover and support ring providing a central opening for an inwardly-opening socket forming a bearing housing, the improvement wherein each blade is rotatably supported in said hub by a radiallyextending blade axle fixed at its inner end to the hub and terminating at its outer end in an enlarged end portion within said bearing housing, the axle projecting through the central opening of said socket, said axle being selected of a length to space said bearing housing radially outward from said hub with clearance therebetween, said connecting means being disposed in said clearance space and connected to blades adjacent said inwardly-open socket, said blade being rotatably mounted on said axle by a single axial ball bearing hav ing a pair of annular race rings surrounding said axle and having one race ring bearing against said enlarged end portion and fitted within said bearing housing, and having the other race ring bearing against said housing cover and support ring whereby said axial ball bearing receives the centrifugal force of said blade as the fan is rotated within said casing, and a spring washer compressed between said enlarged end portion of said axle and the bottom of said bearing housing, said washer having a cross section corresponding to the cross section of said housing to urge said blade outwardly against the single axial ball bearing when said fan is at rest, the size of said fan being determined by the diameter of said casing and the length of said blade axles. 

1. An apparatus for effecting axial flow comprising a generally cylindrical casing, said casing being selected with a diameter corresponding to the desired size of fan, a rotary fan mounted coaxially in said casing having a rotary hub adapted to be mounted on the end of a drive shaft and a plurality of radial fan blades, means to change the pitch of said blades during operation including a dog member mounted outboard of said shaft end rotatable with said hub and displaceable axially relative thereto, and means connecting each of said fan blades to said dog member to determine a pitch position responsive to axial displacement of said dog member, each of said radial fan blades having at its inner end a housing cover and support ring providing a central opening for an inwardly-opening socket forming a bearing housing, the improvement wherein each blade is rotatably supported in said hub by a radially-extending blade axle fixed at its inner end to the hub and terminating at its outer end in an enlarged end portion within said bearing housing, the axle projecting through the central opening of said socket, said axle being selected of a length to space said bearing housing radially outward from said hub with clearance therebetween, said connecting means being disposed in said clearance space and connected to blades adjacent said inwardlyopen socket, said blade being rotatably mounted on said axle by a single axial ball bearing having a pair of annular race rings surrounding said axle and having one race ring bearing against said enlarged end portioN and fitted within said bearing housing, and having the other race ring bearing against said housing cover and support ring whereby said axial ball bearing receives the centrifugal force of said blade as the fan is rotated within said casing, and a spring washer compressed between said enlarged end portion of said axle and the bottom of said bearing housing, said washer having a cross section corresponding to the cross section of said housing to urge said blade outwardly against the single axial ball bearing when said fan is at rest, the size of said fan being determined by the diameter of said casing and the length of said blade axles. 